Filter elements are generally well known in the art and commonly used for filtering liquids and gases. There are several different types of filter elements currently available in the market, each advantageous in one respect or another, depending on the type of filtration for which it is to be used. For example, one well known type of filter element includes hollow, generally tubular, self-supporting resin impregnated and bonded fiber structures. Preferred embodiments of such filters are described in Anderson U.S. Pat. Nos. 2,539,767 and 2,539,768 and are produced and sold by the Assignee herein under the trademark MICRO-KLEAN (Cuno, Incorporated, Meriden, Conn.) wherein the bonding system is a thermosetting resin. Broadly, these filter elements are relatively rigid, self-supporting, thick-walled, tubular members composed entirely of a resin impregnated and bonded fibrous material.
Another type of filter element is also a hollow, tubular, self-supporting structure as mentioned above but an all thermoplastic polymeric bonded fiber structure. Preferred embodiments of such filters are described in Nakajima et al. U.S. Pat. Nos. 4,100,009 and 4,197,156, and are produced and sold by the Assignee herein under the Trademark Betapure.
Another type of filter element is a pleated or convoluted type filter element. Embodiments of these filters are more fully described in Landree U.S. Pat. No. 3,720,323 and Brownell U.S. Pat. No. 4,464,263. These filter elements may also be self-supporting, although they can also be used with supporting members. The disclosure will be specifically directed toward the resin impregnated and bonded fiber type filter elements. However, it will be understood that any type filter element may be substituted therefor. In any event, whatever type of filter element is employed, it is generally used for filtering liquids and gases by flowing radially inwardly under a differential pressure.
Typically, these filter elements have been adapted to be sealingly clamped in a filter housing. In the past, a sealing surface of the filter housing was required to engage the end of the filter cartridge element in order to provide a seal and to prevent by-pass of the contaminants being filtered from the fluid. Typically, the sealing surface was a circular sealing lip or knife edge protruding from the housing which engaged the end of the filter element and was concentric with the axis of the filter. A sealing surface engaged each end of the filter cartridge element. The sealing surface was embedded into the end of the fibrous structure to provide a seal between the edge and the filter element. A compression spring means or clamping means was then used to provide sufficient force to embed the sealing surface of the housing into the end of the filter cartridge element.
Alternately, there are filter housing and cartridge designs, which do not use either a sealing edge or an independent spring or clamping means to provide for the seal between the filter housing and cartridge. These designs feature filter cartridges which have a spring and seal integrally built into the cartridge construction and seal against flat, smooth surfaces in the filter housing. Upon installation, the filter cartridge is compressed between the cover and base of the filter housing and the integral spring combined with the filter media provides the initial sealing force at the end seals of the filter cartridge. However, differential pressure acts directly against this cartridge sealing force which effectively reduces the sealing force and eventually allows bypass to occur. Examples of this type of filter cartridge construction are the Peco Filter-Tex.TM. cartridge and the Pall Profile PRS series filters.
Attempts have been made to solve this problem, some more successfully than others. For example, the Assignee of the present invention has developed a gasket having a melt surface which abuts the filter element. The opposite surface coacts with the sealing surfaces of the housing to provide the necessary seal. Such a gasket and method for its manufacture are the subjects of U.S. Pat. Nos. 5,015,316 and 5,028,327 to Ostreicher et al.
Another problem associated with these types of filter cartridge elements is that it is often difficult to seal effectively. Various means are known for sealing the ends of filters, but most, if not all, of these means cannot be readily used with the preferred type of filter element described herein and/or are expensive and inefficient in use. For instance, Cox et al. U.S. Pat. No. 2,726,184 describes a method for improving the end seals of a pleated or convoluted type filter element. The method includes depositing an amount of unpolymerized, thermosetting adhesive in liquid form on the surface of end discs, allowing the deposited adhesive to harden, and then press fitting the end discs onto the end of the filter element. The adhesive may be in the form of a precut solid adhesive ring which may be placed in the disc. This method is complicated and expensive and requires preformed end discs to be sealed to the end of the filter element.
Another example is Kasten et al. U.S. Pat. No. 2,771,156, which describes a pleated filter element and resilient plastic end caps, the pleated filter element being embedded therein. In a process of molding the end cap, the ends of the pleated element are immersed in a mold filled with a plastic composition and cured. When the filter element is removed from the mold, the ends of the pleats are covered with a tough rubber-like product, i.e., "plastisol"--a vinyl resin with fillers, pigments, plasticizers and/or stabilizers.
In addition, Gershenson et al. U.S. Pat. No. 5,075,004 discloses a filter apparatus having a filter bag with a sealing gasket made out of a thermoplastic elastomeric material. The gasket is formed such that, as the cover plate of the apparatus is closed, the top lip portion of the gasket deflects to form a seal against the cover plate. Notably, however, such a seal is sewn onto a filter bag and not attached to a filter element. Moreover, it is clear that the inwardly directed top portion would not have the desired sealing effect on the conventional filter elements described hereinabove, which require the fluid to flow radially inwardly.
Notwithstanding these sealing methods, it is clear that the art has not provided a facile means or device by which to seal the filter element to the housing without the need for some sort of spring or clamping means and/or the sealing surface. Clearly, in Kasten et al. as well as Ostreicher et al., some sort of clamping device is employed to keep the sealing surface of the housing in contact with the various gasket-like means disposed at the ends of the filter element.
Accordingly, there is a well defined industrial need for a seal which will eliminate the need for the housing to have a sealing surface and which will adequately replace the conventional spring and clamping assemblies employed with most filtration apparatus.